PCM (Pulse Coded Modulation) systems are conventionally known for use in the recording and reproducing of sound signals such as speech and music.
An improved PCM system, i.e., an ADPCM (Adaptive Differential Pulse Coded Modulation) system, is also known.
A PCM system suffers from the problem that the amount of information to be stored is large.
On the other hand, an ADPCM system suffers from the problem that since the differential data between adjacent sound data is stored, it is impossible to follow a waveform having an amplitude that abruptly changes.